Phase 7 follow-up #246 — Phase7Composer + Program.cs wire-in

Activates the Phase 7 engines in production. Loads Script + VirtualTag +
ScriptedAlarm rows from the bootstrapped generation, wires the engines through
the Phase7EngineComposer kernel (#243), starts the DriverSubscriptionBridge feed
(#244), and late-binds the resulting IReadable sources to OpcUaApplicationHost
before OPC UA server start.

## Phase7Composer (Server.Phase7)

Singleton orchestrator. PrepareAsync loads the three Phase 7 row sets in one
DB scope, builds CachedTagUpstreamSource, calls Phase7EngineComposer.Compose,
constructs DriverSubscriptionBridge with one DriverFeed per registered
ISubscribable driver (path-to-fullRef map built from EquipmentNamespaceContent
via MapPathsToFullRefs), starts the bridge.

DisposeAsync tears down in the right order: bridge first (no more events fired
into the cache), then engines (cascades + timers stop), then any disposable sink.

MapPathsToFullRefs: deterministic path convention is
  /{areaName}/{lineName}/{equipmentName}/{tagName}
matching exactly what EquipmentNodeWalker emits into the OPC UA browse tree, so
script literals against the operator-visible UNS tree work without translation.
Tags missing EquipmentId or pointing at unknown Equipment are skipped silently
(Galaxy SystemPlatform-style tags + dangling references handled).

## OpcUaApplicationHost.SetPhase7Sources

New late-bind setter. Throws InvalidOperationException if called after
StartAsync because OtOpcUaServer + DriverNodeManagers capture the field values
at construction; mutation post-start would silently fail.

## OpcUaServerService

After bootstrap loads the current generation, calls phase7Composer.PrepareAsync
+ applicationHost.SetPhase7Sources before applicationHost.StartAsync. StopAsync
disposes Phase7Composer first so the bridge stops feeding the cache before the
OPC UA server tears down its node managers (avoids in-flight cascades surfacing
as noisy shutdown warnings).

## Program.cs

Registers IAlarmHistorianSink as NullAlarmHistorianSink.Instance (task #247
swaps in the real Galaxy.Host-writer-backed SqliteStoreAndForwardSink), Serilog
root logger, and Phase7Composer singleton.

## Tests — 5 new Phase7ComposerMappingTests = 34 Phase 7 tests total

Maps tag → walker UNS path, skips null EquipmentId, skips unknown Equipment
reference, multiple tags under same equipment map distinctly, empty content
yields empty map. Pure functions; no DI/DB needed.

The real PrepareAsync DB query path can't be exercised without SQL Server in
the test environment — it's exercised by the live E2E smoke (task #240) which
unblocks once #247 lands.

## Phase 7 production wiring chain status
- ✅ #243 composition kernel
- ✅ #245 scripted-alarm IReadable adapter
- ✅ #244 driver bridge
- ✅ #246 this — Program.cs wire-in
- 🟡 #247 — Galaxy.Host SqliteStoreAndForwardSink writer adapter (replaces NullSink)
- 🟡 #240 — live E2E smoke (unblocks once #247 lands)

src/ZB.MOM.WW.OtOpcUa.Server/OpcUa/OpcUaApplicationHost.cs

@@ -34,9 +34,11 @@ public sealed class OpcUaApplicationHost : IAsyncDisposable
     // Phase 7 Stream G follow-up (task #239). When composed with the VirtualTagEngine +
     // ScriptedAlarmEngine sources these route node reads to the engines instead of the
     // driver. Null = Phase 7 engines not enabled for this deployment (identical to pre-
-    // Phase-7 behaviour).
-    private readonly ZB.MOM.WW.OtOpcUa.Core.Abstractions.IReadable? _virtualReadable;
-    private readonly ZB.MOM.WW.OtOpcUa.Core.Abstractions.IReadable? _scriptedAlarmReadable;
+    // Phase-7 behaviour). Late-bindable via SetPhase7Sources because the engines need
+    // the bootstrapped generation id before they can compose, which is only known after
+    // the host has been DI-constructed (task #246).
+    private ZB.MOM.WW.OtOpcUa.Core.Abstractions.IReadable? _virtualReadable;
+    private ZB.MOM.WW.OtOpcUa.Core.Abstractions.IReadable? _scriptedAlarmReadable;
 
     private readonly ILoggerFactory _loggerFactory;
     private readonly ILogger<OpcUaApplicationHost> _logger;
@@ -75,6 +77,24 @@ public sealed class OpcUaApplicationHost : IAsyncDisposable
 
     public OtOpcUaServer? Server => _server;
 
+    /// <summary>
+    ///     Late-bind the Phase 7 engine-backed <c>IReadable</c> sources. Must be
+    ///     called BEFORE <see cref="StartAsync"/> — once the OPC UA server starts, the
+    ///     <see cref="OtOpcUaServer"/> ctor captures the field values + per-node
+    ///     <see cref="DriverNodeManager"/>s are constructed. Calling this after start has
+    ///     no effect on already-materialized node managers.
+    /// </summary>
+    public void SetPhase7Sources(
+        ZB.MOM.WW.OtOpcUa.Core.Abstractions.IReadable? virtualReadable,
+        ZB.MOM.WW.OtOpcUa.Core.Abstractions.IReadable? scriptedAlarmReadable)
+    {
+        if (_server is not null)
+            throw new InvalidOperationException(
+                "Phase 7 sources must be set before OpcUaApplicationHost.StartAsync; the OtOpcUaServer + DriverNodeManagers have already captured the previous values.");
+        _virtualReadable = virtualReadable;
+        _scriptedAlarmReadable = scriptedAlarmReadable;
+    }
+
     /// <summary>
     ///     Builds the <see cref="ApplicationConfiguration"/>, validates/creates the application
     ///     certificate, constructs + starts the <see cref="OtOpcUaServer"/>, then drives